ES2749869T3 - Energy efficient fractionation procedure to separate reactor effluent from TOL / a9 + transalkylation procedures - Google Patents

Abstract

A process comprising the steps of: (a) supplying a pre-fractionation column feed stream comprising toluene, C8 aromatics, and C9 + aromatics to a reboiled pre-fractionation column to produce an upper stream from the pre-fractionation column and a lower stream of the pre-fractionation column; and (b) supplying a top stream from the pre-fractionation column and a bottom stream from the pre-fractionation column to a side discharge column to produce a top stream from the side discharge column comprising toluene, and a side stream from the column. lateral discharge comprising C8 aromatics.

Description

DESCRIPTION

Energy efficient fractionation procedure to separate reactor effluent from TOL / A9 + transalkylation procedures

BACKGROUND

[0001] Aromatic complexes often derive their feeds from a catalytic reformer, although other feeds of mixed xylenes feeds such as those derived from pyrolysis gasoline from olefin crackers are also possible. The reformed reformer product contains benzene (Bz), toluene (TOL), C8 aromatics (ethylbenzene (EB), and the three isomers of xylene-paraxylene (pX), metaxylene (mX), and orthoxylene (oX)) -, and C9 + aromatics that are mainly C9 and, to a lesser extent, C10 + aromatics. Most aromatics complexes focus on the production of paraxylene and benzene and, occasionally, orthoxylene and metaxylene, although the markets for orthoxylene and metaxylene are not as large as for paraxylene. Paraxylene oxidizes to terephthalic acid, which is purified and polymerized with ethylene glycol to make polyester. Polyester is used to make clothes, film and bottles. Benzene is used to make many useful derivatives with end products such as polystyrene, nylon, polycarbonate, and phenolic resins.

[0002] To get the most out of paraxylene and benzene from a given reforming amount, aromatic complexes can comprise units that convert toluene and / or C9 + aromatics into xylene and benzene reforming, including transalkylation units of TOL / A9 + (TA of TOL / A9 +).

[0003] The TOL / A9 + transalkylation procedure usually takes place in the presence of hydrogen. The processing of C9 + aromatics is complex, since there are various A9 and A10 isomers that can go through various reactions depending on the chosen catalyst. Reactions taking place in a TOL / A9 + transalkylation (TA) reactor include, without limitation:

TOL TOL Bz • XYL (1)

MEB 112 •> TOL C2 (2)

TOL TMB - 2 XYL (3)

C3Bz H2. - »Bz C3 (4)

DMEB + 112 •> XYL C2 (5)

DEB + H2 -> EB C2 (6)

EB C2 - »Bz C2 (7)

C4Bz 112 Bz -i- C4 (8)

C3XYL 112 XYL C3 (9)

TMB -i- TOL = i TMB Bz (10)

Where:

XYL = xylene isomers

MEB = methylethylbenzenes (3 isomers)

TMB = trimethylbenzenes (3 isomers)

C3Bz = propylbenzenes (isopropylbenzene = cumene and n-propylbenzene)

H2 = hydrogen

C2 = ethane

C3 = propane

DMEB = dimethylethylbenzenes (6 isomers)

DEB = diethylbenzenes (3 isomers)

C4Bz = butylbenzenes (4 isomers)

C3XYL = propylxylenes (includes n-propyl xylenes and isopropyl xylenes known as cymenes)

TTMB = tetramethylbenzenes (3 isomers)

[0004] Note that MEB hydrocracking (Reaction 2) produces TOL, which can react with TMB to form xylenes (Reaction 3) or disproportionate to form xylenes and benzene (Reaction 1). Thus, A9 + can be a feed for only one TOL / A9 + reactor, that is, the TOL in the feed can be zero.

[0005] Hydrocracking of MEB and propylbenzene (Reactions 2 and 4) can lead to very high conversion. However, transalkylation reactions that produce xylene isomers (such as Reactions 1 and 3) are limited by equilibrium. Thus, the effluent from the TOL / A9 + TA reactor will contain volatile fractions, including C2 and C3, Bz, XYL, and unreacted TOL and A9 +. The reactor effluent is separated into streams rich in volatile fractions, Bz, XYL, and unreacted TOL and A9 +. TOL and a 9+ components are recycled to the reactor. Separation of the reactor effluent into these streams consumes a lot of energy and represents a substantial portion of the variable cost for these processes.

[0006] Consequently, there is a need for other cheaper and lower energy consumption schemes to separate the reactor effluent from the TOL / A9 + transalkylation reactors.

[0007] US patent 2012/0271084 discloses methods for producing Cs aromatic hydrocarbons by transalkylation of C ⁷ and C ⁹ aromatic hydrocarbons. US patent 2013/0261365 discloses a method in which xylenes are produced by transalkylation of a heavy reformer.

SUMMARY

[0008] The present disclosure refers to the separation of low energy consumption of the effluent from a TA reactor of TOL / A9 + in streams concentrated in volatile fractions, benzene, TOL, AS and A9 +. In one aspect, the disclosure is directed to a process that includes (a) providing a pre-fractionation column feed stream including toluene, CS aromatics, and C9 + aromatics to a reboiler pre-fractionation column to produce a higher stream of the pre-fractionation column and a lower stream of the pre-fractionation column; and (b) providing the top stream of the pre-fractionation column and the bottom stream of the pre-fractionation column to a side discharge column to produce a top stream of the side discharge column including toluene, and a first side stream of the side discharge column including CS aromatics. The method may also include producing a bottom stream from the side discharge column including C9 + aromatics. Alternatively, the process may include the production of a second lateral discharge column side stream including A9 for recycling to a TOL / A9 + transalkylation reactor without further fractionation, and a lower C10 + side discharge column stream containing a weight percent concentration less than about 2%, that is, substantially free of A9.

[0009] In various aspects of the disclosure, the method includes recovering the paraxylene from the first side stream from the side discharge column including CS aromatics to produce a paraxylene product stream and a paraxylene lean stream.

[0010] In a particular aspect of the disclosure, a benzene column feed stream including benzene, toluene, CS aromatics, and C9 + aromatics is provided to a benzene column to produce a top stream including benzene and a stream. bottom of the benzene column including toluene, CS aromatics, and C9 + aromatics, where the bottom stream of the benzene column is the feed stream from the pre-fractionation column.

[0011] In another aspect, the benzene column feed stream is obtained by a process including providing a stabilizer column feed stream including volatile fractions, benzene, toluene, CS aromatics and C9 + aromatics to a stabilizer column. to produce an upper stabilizer column stream (s) including volatile fractions and a lower stabilizer column stream including benzene, toluene, C ^s aromatics and C9 + aromatics, where the bottom stabilizer column stream is the feed stream of the benzene column.

[0012] In these and other aspects of the disclosure, the method may include mixing a transalkylation reactor effluent stream including volatile fractions, benzene, toluene, CS aromatics and C9 + aromatics with a paraxylene unit stream including benzene and toluene to produce the feed stream from the stabilizer column.

[0013] In one aspect, the method includes operating the side discharge column at a pressure above atmospheric pressure and using the condensation vapors from the upper stream of the side discharge column to generate steam, to reboil the column. benzene and / or reboil the stabilizer column.

[0014] Another embodiment of the disclosure is directed to an apparatus including a reboiled pre-fractionation column to receive a pre-fractionation feed stream including toluene, CS aromatics, and C9 + aromatics and to produce an upper prefractionation column stream and stream bottom of pre-fractionation column; and a side discharge column to receive the upper stream of the pre-fractionation column and the bottom stream of the pre-fractionation column and produce a top stream from the side discharge column including toluene, and a first side stream from the side discharge column including C8 aromatics. In various aspects of this embodiment, the side discharge column further produces a bottom stream from the side discharge column that includes C9 + aromatics. Alternatively, the side discharge column further produces a second discharge column side stream including A9 for recycling to a TOL / A9 + transalkylation reactor without further fractionation, and a bottom stream of the C10 + side discharge column containing a weight percent concentration less than about 2% A9.

[0015] In another aspect, the apparatus includes a benzene column for receiving a benzene column feed stream including benzene, toluene, C8 aromatics, and C9 + aromatics, and separating the benzene column feed stream into an upper stream from the benzene column including benzene and a lower stream from the benzene column including toluene, C8 aromatics and C9 + aromatics, where the lower stream of the benzene column is the pre-fractionation column feed stream.

[0016] The apparatus may also include a stabilizer column to receive a stabilizer column feed stream that includes volatile fractions, benzene, toluene, C8 aromatics, and C9 + aromatics, and produce a stabilizer column top stream that includes volatile fractions and a stabilizer column downstream including benzene, toluene, C8 aromatics and C9 + aromatics; where the bottom stream of the stabilizer column is the feed stream of the benzene column.

[0017] The apparatus may also include a mixer for mixing a transalkylation reactor effluent stream including volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics with a paraxylene unit stream including benzene and toluene to produce the stream of stabilizer column feed.

[0018] The apparatus may also comprise a paraxylene recovery section for recovering paraxylene from a side stream of the side discharge column comprising C8 aromatics, preferably where the paraxylene recovery section comprises a selective paraxylene absorption unit, or preferably where the paraxylene recovery section comprises a crystallization unit.

[0019] The apparatus may further comprise a transalkylation reactor for reacting a reactor feed stream comprising toluene and optionally C9 + aromatics to produce a transalkylation reactor effluent stream comprising volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics.

[0020] The side discharge column can receive the upper stream from the pre-fractionation column as a steam stream without condensation. The pre-fractionation column and the side discharge column can share a common frame with a partition wall.

[0021] In another embodiment, the disclosure is directed to a process including the following steps: reacting in a transalkylation reactor a reactor feed stream including toluene and optionally C9 + aromatics to produce a effluent stream from the transalkylation reactor including volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics; optionally mixing the effluent stream from the transalkylation reactor with a stream from the paraxylene unit including benzene and toluene to produce a stabilizer column feed stream including volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics; separating the stabilizer column feed stream into a stabilizer column to produce an upper stabilizer column stream including volatile fractions and a lower stabilizer column stream including benzene, toluene, C8 aromatics and C9 + aromatics; separating the bottom stream from the stabilizer column into a benzene column to produce a top stream from the benzene column including benzene and a bottom stream from the benzene column including toluene, C8 aromatics and C9 + aromatics; providing the bottom stream from the benzene column to a reboiled pre-fractionation column to produce a top stream from the pre-fractionation column and a bottom stream from the pre-fractionation column; providing the top stream from the pre-fractionation column and the bottom stream from the pre-fractionation column to a side discharge column to produce a top stream from the side discharge column including toluene, and a side stream from the side discharge column that include C8 aromatics; recovering paraxylene from the side stream of the side discharge column including C8 aromatics; and recovering benzene from the top stream of the benzene column, where at least a portion of the top stream from the side discharge column contains toluene and one stream from the side discharge column containing C9 + aromatics is recycled to the transalkylation reactor.

[0022] The side discharge column may further produce a bottom discharge column stream comprising C9 + aromatics where at least a portion of this stream is recycled to the transalkylation reactor. The side discharge column can receive the upper stream from the pre-fractionation column as a steam stream without condensation. The pre-fractionation column and the Side discharge can share a common frame with a partition wall.

[0023] The method may further comprise producing a second lateral discharge column stream comprising A9, of which at least a portion is recycled to a TOL / A9 + transalkylation reactor without further fractionation, and a bottom stream of the C10 + side discharge column containing a weight percent concentration of approximately 2% A9. The side discharge column can operate at a pressure above atmospheric pressure and the benzene column can reboil by condensation of at least a portion of the upper stream from the side discharge column. the stream can be generated from the condensation of at least a portion of the top stream from the discharge column.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]

Figure 1 shows an integrated aromatics complex for paraxylene recovery by a selective PAREX ™ absorption procedure. The effluent from the TOL / A9 + transalkylation reactor is separated into concentrated streams in benzene, TOL, C8A and C9A + by sequential Bz, TOL, Xylene splitter and A9 columns.

Figure 2 shows a separation plan to separate concentrated streams into volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics. The plan includes a reboiled pre-fractionation column fed by the bottom stream of a benzene column including toluene, C8 aromatics, and C9 + aromatics. The upper and lower streams of the reboiled pre-fractionation column are introduced into the side discharge column, which produces an upper stream of the side discharge column including toluene, a side stream of the side discharge column including C8 aromatics, and a bottom stream from the side discharge column including C9 + aromatics.

Figure 3 shows a plan where the A9 + material for recycling to the TOL / A9 + TA reactor is taken as an additional side discharge from the side discharge column. the bottom stream of the side discharge column includes C10 +.

[0025] Those skilled in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity, and that they have not necessarily been drawn to scale. For example, the dimensions of some of the elements appearing in the figures may be exaggerated with respect to other elements to allow a better understanding of the embodiment or embodiments of the present invention. Those skilled in the art will also understand that certain elements shown in these figures may represent sections of an aromatic complex comprising various equipment and unit operations, such as reactors, pumps, distillation columns, pumps, compressors, heat exchangers. and separation equipment, such as filters, centrifuges, selective absorption chambers and the like.

DESCRIPTION

[0026] The disclosure refers to a low energy fractionation procedure for separating the effluent from a TOL / A9 + transalkylation (TA) reactor into streams concentrated in volatile fractions, benzene, a stream concentrated in TOL that can be recycled to the reactor, a concentrated stream of C8 aromatics (A8 or C8A) that can be sent directly to a paraxylene recovery unit by crystallization or selective absorption without the need for additional fractionation, and an A9 + stream that can be further fractionated, optionally, to recover aromatics C9 (A9 or C9A) and C10 aromatics (A10 or C10A) to recycle to the TOL / A9 + TA reactor.

[0027] The methods and apparatus disclosed in this invention provide certain advantages and advances over the prior art. For example, the volatile fractions and benzene are separated on a stabilizer column and a benzene column respectively. The bottom streams of the TOL, A8, and A9 + benzene column (TOL / A8 / A9 +) are then separated into separate streams rich in those components using an apparatus that includes a reboiled pre-fractionation column and a side discharge column that produces : 1) a stream from the upper plate concentrated in TOL; 2) a stream concentrated in A9 +, the streams of which can be recycled to the reactor; and 3) a side discharge stream concentrated in A8 and substantially free of benzene, TOL, and A9 + that can be directed to a pX separation unit by crystallization or selective absorption for recovery of the pX product. The pressure of the reboiled pre-fractionation column and the side discharge column can be increased so that condensed top plate vapors from the side discharge column can be used to reboil the stabilizer and / or the benzene column and, optionally, to generate current. Steam from the top plate of the pre-fractionation column can be introduced into the side discharge column without condensation, thus eliminating the need for a condenser, a backflow drum, and associated equipment. An additional lateral discharge stream can be taken from the concentrated lateral discharge column at A9 and optionally A10 which can be recycled to the reactor. In this case, the bottom stream of the discharge column includes C10 + hydrocarbons that can be used for fuel or other uses. This avoids the need for a separate A9 column and saves additional energy.

[0028] Those skilled in the art will appreciate that the designator "CX" refers to a compound that includes X carbon atoms, "CX +" refers to a compound that includes X or more carbon atoms, and "CX" refers to to a compound that includes X or fewer carbon atoms. The term "AX" is used to designate a stream that includes aromatics with X carbon atoms. For example, A9 + can be used to designate a stream that includes aromatics with nine or more carbon atoms. "CX aromatics" or "CXA" refers to a mixture of aromatic and non-aromatic compounds with X atoms. Thus, for example, "C8 aromatics" or "C8A" designates a stream of aromatic and non-aromatic compounds with 8 carbon atoms. Similarly, "C8 +" may contain some A8 + and non-aromatics with more than 8 or more carbon atoms.

[0029] Xylenes mix is a term used for a stream that includes not only xylene isomers, but also ethylbenzene (EB), which has the same molecular formula as xylene isomers (C ⁸ H ¹⁰ ), but is an isomer structural bearing an ethyl group attached to a benzene, instead of two methyl groups in the case of xylene isomers. There are three xylenes isomers: orthoxylene (oX), metaxylene (mX), and paraxylene (pX). Collectively, the xylene isomers are designated C8 or C8A aromatics. The boiling points of C8As are very close, so it is neither practical nor economical to separate the pX from the mixed xylenes by distillation. Thus, pX is separated from C8A by procedures such as crystallization or selective absorption of pX.

[0030] As used in this invention, the phrase "substantially free of" generally refers to a percent concentration by weight less than about 2% of a component, more specifically, a percent concentration lower by weight, about 1.5% of the component, eg, a weight percent concentration less than about 1.0% of the component if the pX separation unit is a crystallization unit. In one embodiment, if the pX separation unit is a pX selective absorption unit, substantially A9 + free it means less than about 500 ppm by weight, about 400 ppm by weight, about 300 ppm by weight, about 200 ppm by weight or approximately 100 ppm by weight of A9 + or as required for the feed stream to the pX separation unit.

[0031] As used in this invention, the phrase "a stream concentrated in one aromatic component or components" refers to a stream that includes such components and is substantially free of other aromatic components. For example, a benzene-concentrated stream means a stream that includes mainly benzene and is substantially free of TOL, A8, and A9 +. a stream concentrated in C8A + means a stream that mainly includes C8A and C9A + but substantially free of benzene and TOL.

[0032] Figure 1 illustrates an aromatics complex including a plan for separation of reactor effluent from a TA unit of TOL / A9 +. This aromatic complex includes several units including a naphtha hydrotreating unit (NHT); a reformer, such as a UOP CCR PLATFORMING ™ unit; an extraction unit, such as a UOP SULFOLANE ™ Extraction Unit; a TOL / A9 + AT unit, such as a UOP TATORAY ™ unit; a paraxylene unit that further includes a xylene isomerization unit, such as a UOP ISOMAR ™ unit for isomerizing xylene isomers and converting ethylbenzene (EB); a selective pX absorption unit, such as a UOP PAREX ™ unit; and distillate columns to separate the reactor effluent from the TA unit of TOL / A9 + and the xylene isomerization unit in streams rich in benzene, TOL, C8A and C9A +. The more detailed description of various aspects of this aromatic complex and the units it can comprise can be found in RA Meyers, editor, Handbook of Petroleum Refining Processes, 3rd Edition, Mc-Graw-Hill (2004), which is incorporated in its entirety in this invention.

[0033] In Figure 1, a naphtha stream (stream 1) including C6-C10 paraffins and naphthenes is introduced into a naphtha hydrotreating unit (NHT) 2. The NHT 2 unit includes a reactor that reacts sulfide and nitrogen they contain components with hydrogen (stream not shown) and typically remove sulfur and nitrogen compounds as light gaseous products such as hydrogen sulfide and ammonia (also not shown). the hydrotreated naphtha stream (stream 3) is sent to a reformer 4. The reformer unit 4 includes a reactor that cyclizes straight and branched chain paraffins to form naphthenes and dehydrogenation of the naphthenes to form aromatic compounds . The reformer generates a stream rich in hydrogen 5 and volatile fractions 6, and a stream that includes aromatic-rich C5 + hydrocarbons (stream 7) including benzene, toluene, C8 aromatics, and C9 + aromatics. stream 7 is introduced into a reforming separator column 8. Reforming separator column 8 generates an upper plate stream (stream 9) rich in C7 hydrocarbons including benzene and toluene, and a lower stream including C8 + aromatics (stream 10 ). stream 9 is introduced into an extraction unit 11 that separates the refined stream (stream 12) that includes mainly non-aromatics C5-C7 that is aromatic-poor and the extraction stream (stream 13) that is rich in benzene and toluene and it is substantially free of non-aromatics. stream 13 is combined with the liquid effluent from a TOL / A9 + 14 transalkylation unit (TA). The TOL / A9 + 14 TA unit includes a reactor that converts at least a portion of the TOL and A9 + into products that include benzene and xylene isomers by reactions including Reactions 1-10 (above). The TOL / A9 + 14 unit consumes hydrogen from a hydrogen rich feed stream (not shown), and generates volatile fractions (not shown). Volatile fractions can be removed with a stabilizer (not shown), which can be part of the TOL / A9 + unit.

[0034] The effluent from the stabilized reactor of the TA unit of TOL / A9 + 14 (stream 15) includes benzene, unreacted TOL, C8A and unreacted C9A +. stream 15 combines with the stream from extraction unit 11 (stream 13) to produce stream 16. The benzene, TOL, C8A, and C9A + from stream 16 combined are separated into the sequential distillation columns of benzene, toluene, xylene splitter and A9 17, 20, 24, and 38. Figure I shows the optional co-production of an orthoxylene product as the top plate of the oX 35 column.

[0035] Stream 16 is directed to a benzene column 17, which produces an upper plate stream that includes benzene (benzene product stream 18) and is substantially free of other aromatics, and a lower stream (stream 19) that includes C7 + aromatics. stream 19 is directed to a TOL column 20, which produces a top plate stream (stream 21) that includes TOL and is substantially free of other aromatics and is directed to the TA unit of TOL / A9 + 14, and a bottom stream (stream 22) including C8 + aromatics.

[0036] Stream 22 mixes with the bottom stream a de-phanizing column 32 (stream 34) and the bottom stream of reforming separator 8 (stream 10) to form a feed stream (stream 23) directed to the xylene spacer column. 24. Column 24 produces an upper plate stream that includes C8A and some TOL (stream 25) and is substantially free of other aromatics and a lower stream (stream 26) that includes C9A +, and in this case includes a substantial fraction of the oX in a combined xylene separator column feed stream (stream 23). Orthoxylene is produced as the top plate product from column 35. Co-production of oX within the aromatic complex is optional. the bottom stream from column 35 including A9 + is directed to column A9 38 which produces a top plate stream 39 comprising A9 and typically some A10 that is recycled to the TA unit of TOL / A9 +. the bottom stream from column 38 comprising C10 + is taken as a product for use as a fuel, for example, or for other uses.

[0037] In one embodiment of the diagram shown in Figure 1, the condensation vapors from the xylene (XS) separator of an aromatic complex including a selective absorption unit of pX PAREX ™ can be used to reboil the extract columns and refined within the PAREX ™ unit section (not shown). Thus, there may not be enough additional heat available in the XS condensation vapors in the upper plate to boil the benzene column or toluene column in the TOL / A9 + transalkylation unit.

[0038] stream 25 is directed to a pX recovery unit 27 as a UOP PAREX ™ unit, which produces a high purity pX product (stream 28), and a refining stream (stream 29) that is poor in pX. When the pX recovery unit is a UOP PAREX ™ unit, it can also produce a TOL rich stream (not shown) from co-absorbed TOL which can be directed to the TOL / A9 + 14 TA unit. The lean refining stream in pX (stream 29) it is directed to a xylene isomerization unit 30 that includes a reactor that isomerizes the xylenes from the pX-poor raffinate to a near-equilibrium distribution, and converts at least a portion of the EB and xylene isomers, or benzene and ethane. Xylene isomerization catalysts that convert EB primarily to xylene isomers or benzene and ethane are known to those skilled in the art. Xylene isomerization and EB conversion reactions usually take place in the vapor phase, consume hydrogen from a hydrogen rich feed stream (not shown), and can generate a hydrogen rich vent stream (not shown). However, it is known that the xylene isomerization and EB conversion processes are conducted in the liquid or supercritical phases without the addition of hydrogen.

[0039] The effluent from the reactor (stream 31) from the xylene isomerization unit 30 can be directed to the deptanizing column 32 which produces a stream of C7 (stream 33). stream 33 can be a value stream, liquid, or both. stream (s) 33 may comprise benzene and TOL, and may be further stabilized to remove volatile fractions before directing it to benzene column 17 or extraction unit II to recover benzene as product and TOL for recycling to TA unit of TOL / A9 + 14. This stabilizer is not shown in Figure 1.

[0040] a lower current of the de-staptanizer (current 34) includes C8A +. this stream combines with the bottom stream of the reformer separator (stream 10), and the bottom stream of the TOL column 20 (stream 22), which also comprise C8A +, and are directed to the xylene spacer column 24.

[0041] A lower stream of the xylene separator (stream 26) can be directed to an oX column 35 that produces an upper plate stream of oX product (stream 36) and a lower stream (stream 37) including A9 +. stream 37 is directed to a column of A938 that produces a bottom stream (stream 40) that includes C10 + that can be taken as a product for use as, for example, a fuel, and a top plate stream (stream 39) that includes A9 + which can be addressed to the TA unit of TOL / A9 +.

[0042] Returning to Figure 2, an effluent stream from a TOL / A9 + TA unit reactor (not shown) (stream 215) can be combined with an extraction stream from an extraction unit (not shown) (stream 213) to produce a feed stream from the stabilizer column (stream 241). stream 241 can be preheated in exchanger 242 to produce a preheated stream (stream 243) that is directed to a stabilizer column 244. The heat used to preheat stream 241 can be bypassed of a temperate process stream available within the aromatics complex. Stabilizer column 244 produces a top plate vapor stream (stream 245) that includes light steam hydrocarbons, and a bottom stream (stream 247) that includes benzene, TOL, C8A, and C9A +, and can produce a liquid top plate stream (stream 246), which may be a benzene entrainment stream including benzene and non-aromatic benzene boilers.

[0043] Stream 247 can be combined with the extraction stream from an extraction unit (not shown) (stream 213) including benzene and toluene to produce a benzene column feed stream (stream 216). stream 216 is directed to benzene column 217 which produces an upper plate stream (stream 218) that includes benzene and a lower stream (stream 219) that includes TOL, C8A, and C9A +.

[0044] Stream 219 is directed to distillation apparatus 260 with a pre-fractionation column 250, which includes a reboiler 251, and a side discharge column 252. Pre-fractionation column 250 produces an upper plate stream (stream 255). which is directed as a feed to the side discharge column 252. In one embodiment, the top plate stream 255 is preferably a steam stream, but it can be a liquid stream if the prefraction column 250 has a top plate condenser, or it can be a stream of vapor and liquid. The pre-fractionation column 250 also produces a liquid bottom stream (stream 258) which is directed as a feed to the side discharge column 252.

[0045] Side discharge column 252 produces various streams, including a liquid stream (stream 256) employed as a reflux to pre-fractionation column 250, a top plate stream (stream 221) that includes TOL and is substantially C8A + free, a side discharge stream (stream 257) that includes A8 and is substantially free of TOL and A9 +, and a bottom stream (stream 237) that includes C9A + and is substantially free of A8-. the stream including TOL (stream 221) can be recycled to a TA unit of TOL / A9 + (not shown). a bottom stream including A9 + (stream 237) can be directed to a column of A9 (not shown) that can produce a top plate stream that includes A9 and some A10 that can be recycled to a Ta unit of TOL / A9 +, and a bottom stream that includes C10 + and is substantially free of A9 that can be used as, for example, a fuel. Side discharge column 252 includes a reboiler 253 and one or more condensers 254. The condensers can be used to reboil other columns such as stabilizer column 244, benzene column 217, and / or to generate steam.

[0046] Figure 3 is identical to Figure 2, except that (1) an additional side discharge stream (stream 301) is taken from side discharge column 252 which mainly includes A9 and some A10 for recycling to the TA reactor TOL / A9 +, and 2) the bottom stream of the side discharge column (stream 302) including C10 + which can be used as, for example, a fuel. This embodiment eliminates the need for a separate A9 column and further reduces energy and capital consumption for an aromatic complex. the stream that includes A8 and is substantially free of TOL and A9 + (stream 257) can be directed to a pX recovery section to recover the pX product.

[0047] Various embodiments of the pre-fractionation column and the side discharge column are provided in the Examples including examples of locations of trays for feed streams 255 and 258 to the side discharge column, and removal of the reflux stream 256 and side discharge current 257.

[0048] In some embodiments, the pre-fractionation column may be combined into a partitioned wall single frame column with a reboiler for the pre-fractionation side.

[0049] As shown in the examples, the combination of the pre-fractionation column (PREFRAC) and the side discharge column (SD-COL) can be designed to meet the specifications for TOL and A9 + in the A8 side discharge stream so that this current can be sent directly to a unit that separates the pX by selective absorption or crystallization.

[0050] In some aspects of the methods and apparatus disclosed in this invention, the side discharge column and, consequently, the pre-fractionation column are designed to operate at upper plate pressures high enough that the condensation vapors from the Side discharge column can be used to reboil the benzene column, the stabilizer column, and / or generate steam to save more energy. Those of skill in the art will recognize that the temperature of the condensation vapors from the top plate of a column with a total condenser, such as SD-CO ^1, is related to the pressure of the top plate from that column. Similarly, the temperature of the bottom stream of a column is related to the pressure of that column, and thus the pressure of the column determines the minimum temperature of the heating medium that can be used to reboil said column. The pressure of the saturated steam is related to the temperature of the heating medium necessary to generate said steam. In all cases, the higher the pressure, the higher the temperature. The temperature of the condensation vapors from the top plate of a first column must be higher than the temperature of the bottom stream from a second column being boiled by the first column, and must be higher in an amount that provides sufficient pulling force for heat transfer. Thus, the pressure of the upper plate of the lateral discharge column (SD-COL), and, consequently, the pre-fractionation column (PREFRAC) can be increased to provide a temperature of the condensation vapors from the top plate of the SD-COL column of more than about 5 to 25 degrees Celsius, more preferably more than about 10 to 15 degrees Celsius, above the temperature the bottom stream of a column that is being boiled using these vapors, or the saturation temperature of the steam that is being generated. It is possible to increase the pressure of the column above a pressure that provides such temperature differences, but this will increase the necessary wall thickness for the column and thus its cost.

[0051] If the condensation vapors from the SD-COL column are being used to boil the benzene column, the pressure of the top plate of the SD-COL column may be increased, for example, above about 50 psia (345 kPa absolute). If the steam is used for heating process streams within the aromatics complex or for export to other units, it is preferable to increase the pressure of the pre-fractionation and side discharge columns so that this steam can be generated from the condensation vapors of the dish upper side discharge column. The steam that is generated recovers some of the energy introduced into the reboilers of the column as useful energy. To generate medium pressure steam (10 barg), the pressure of the top plate of the SD-COL column can be increased above 115 psia (793 kPa absolute). If the condensation vapors from the top plate of the SD-COL column are only being used to generate low pressure steam (172 kPa absolute (25 psia)), then only the pressure of the top plate of the SD column would have to be increased- COL above about 22 psia (152 kPa absolute). If condensation vapors from the top plate of the side discharge column are being used only to reboil the stabilizer column, the pressure of the top plate from the SD-COL column can be increased above about 115 psia (793 kPa absolute).

[0052] In some embodiments of the methods and apparatus disclosed in this invention, the effluent from a TOL / A9 + reactor is separated by the fractionation schemes of Figures 2 or 3 described above, which are designed to produce a discharge stream A8 side that meets the specification of less than 500 ppmw of A9 + suitable for direct powering a unit that separates the pX by selective absorption. In various embodiments, the A8 side discharge stream contains a weight percent concentration less than about 2% TOL and more specifically a weight percent concentration less than about 1.5% TOL, and can be recovered somewhat via a TOL finishing column within a selective absorption unit (not shown).

[0053] In some embodiments shown in Figures 2 and 3, the stabilizer column 244 is designed as a dehexanizer column where non-aromatic benzene boilers are removed in the top plate streams 245 and 246. In this case, the stream 218 can meet the specifications of the salable benzene product. In other embodiments, the stabilizer column 244 can be designed as a pentanizer where C5 hydrocarbons are removed in the top plate streams 245 and 246, and the benzene-concentrated stream (stream 218) or the bottom stabilizer stream 247 is directed to a unit extraction to remove non-aromatic benzene boilers.

[0054] Units that separate pX by crystallization can tolerate much higher levels of A9 + in their feed. Commercial pX crystallization units operate with a weight percent concentration of approximately 2% A9 + or greater. In another embodiment of this disclosure, the effluent from a TOL / A9 + reactor is separated by the fractionation schemes of Figures 2 and 3 described above and designed to produce a lateral discharge stream of A8 containing a lower weight percent concentration , at approximately 2% A9 +, specifically, a weight percent concentration less than, approximately, 1.5% A9 +, and more specifically, a weight percent concentration less than, approximately, 1.0% A9 + which is suitable for direct feeding to a pX separation section that separates the pX by crystallization. Embodiments employing a crystallization unit for pX separation will require less energy for separation than embodiments employing a selective absorption unit for pX recovery.

[0055] In other embodiments, aromatic complexes including various combinations of conventional toluene disproportionation units (TDP), selective toluene disproportionation units (STDP) that produce pX-rich xylene isomers, and / or TOL / A9 + from the separation scheme of this disclosure.

EXAMPLES

[0056] The following Examples are included for explanatory purposes only, of a non-limiting nature.

[0057] A CX- (light aromatic) pX unit including benzene and TOL and condensate effluent from the TOL / A9 + reactor, whose mass fraction of components appear in Table 1, is used in the examples. TOL / A9 + condensed reactor contains 640 ppmw of naphthalene. Compositions are typical, but as those skilled in the art will know, compositions and flow rates depend on many variables, including the composition of the reformate and the relative size of the pX unit and the TOL / A9 + unit.

Table 1. Typical compositions of the reactor effluent pX unit current

(705 512 Ib / hr equals 320015 kg / hr and 45556 Ib / hr equals 20664 kg / hr.)

[0058] In all the examples, this mixture is preheated and sent to a stabilizing column that eliminates volatile fractions, and then to a benzene column where a concentrated stream of benzene is taken in the upper plate for sale as high benzene. purity or as feed to an extraction unit, where benzene is further purified by removing essentially a non-aromatic refining stream. The behaviors of all columns, including the compositions and conditions of all product column streams, are simulated using an ASPEN Plus® procedure simulator from Aspen Technology, Inc. For all examples, the design of the stabilizer column and the benzene column is the same. Thus, the feed rate and composition of the bottom stream of the benzene column is the same. Typical specifications for the benzene column are 98% benzene recovery on the top plate, and 400 ppmw TOL with Bz base component. The feed rate, composition, and temperature of the bottom stream of the benzene column appear in Table 2.

[0059] The calculated absorbed performance of the benzene column for all examples obtained from the ASPEN Plus® simulations is 79.5 MMBTU / hr (23.3 MW), and the lower stream temperature of that of the Benzene column calculated is about 150 ° C. The calculated absorbed performance of the stabilizer column is 37.7 MMBTU / hr (11.0 MW), and the calculated stabilizer under-stream temperature is about 184 ° C.

Table 2. Feeding rate ^ ossition temperature of the bottom stream of the benzene column

(continuation)

(615507 Ib / hr equals 279189 kg / hr and 301.7 ° F equals 149.8 ° C)

EXAMPLE 1: Separation scheme to produce an A8 stream suitable for direct delivery to a pX recovery unit by selective absorption

[0060] Example 1 demonstrates the production of mixed xylenes by further fractionating the bottom stream of the benzene column according to the fractionation scheme of Figure 1.

[0061] the bottom stream of the benzene column is fed into a simulated toluene column to have 52 theoretical stages with feed to stage 26. The pressure of the steam leaving the top tray is set at 62.3 psia (430 kPa absolute) and the condenser is assumed to have a pressure drop of 5 psi (34.5 kPa). Design specifications are entered into the column simulation of a weight percent concentration of 0.5% C8A in the TOL top plate stream and a weight percent concentration of 1% TOL between C8A in the bottom stream of the column. The performance of the absorbed reboiler calculated from the simulation is 152.6 MMBTU / hr (44.7 MW). The temperature of the condensation vapors in the upper plate of the column is 166.2 ° C, and the calculated operation of the condenser is 125.1 MMBTU / hr (36.7 MW), enough to reboil the benzene column.

[0062] The bottom streams of the toluene column are passed to a simulated xylene (XS) separator column to have 122 theoretical stages with feed to theoretical stage 91 from the top. The pressure of the steam leaving the top tray is set at 85 psia (586 kPa) so that the condensation vapors from the top plate are hot enough to boil the extract and refine columns of a unit that separates the pX by absorption selective. Design specifications are entered into the simulation of the xylene separator column at a weight percent concentration of 0.05% (500 ppmw) of A9 + in the C8A top plate stream and a weight percent concentration of 1 % C8A in the bottom stream of the C9A + column. The performance of the absorbed column reboiler calculated from the simulation is 112.8 MMBTU / hr (33.1 MW).

[0063] Thus, necessary operation of the combined absorbed reboiler 265.4 MMBTU / hr (77.8 MW) to the column and the column TOL XS to perform the desired separation of the underflow from the column benzene in a stream of TOL, a stream of C8A, and a stream of A9 + where the stream of C8A contains a percentage concentration by weight of 1% TOL and meets a specification of 500 ppm A9 + so that this stream can be sent directly to a selective absorption unit for pX separation.

[0064] The A9 + stream can be directed to an A9 column that can produce an upper plate stream that includes A9 and some A10 that can be recycled to a TOL / A9 + TA unit, and a lower stream that includes C10 + and that it is substantially free of A9 which can be used as, for example, a fuel. EXAMPLE 2: Separation scheme to produce an A8 stream suitable for direct delivery to a pX recovery unit by crystallization

[0065] Example 2 demonstrates the production of mixed xylenes by further fractionating the bottom stream of the benzene column according to the fractionation scheme of Figure 1.

[0066] The design of the benzene and toluene columns is the same as in Example 1. The bottom stream of the benzene column is introduced into a simulated toluene column to have 52 theoretical stages fed to stage 26. The Vapor pressure exiting the upper tray is set at 62.3 psia (430 kPa absolute) and the condenser is assumed to have a pressure drop of 5 psi (34.5 kPa). The specifications of design, a weight percentage concentration of 0.5% C8A in the stream of the upper TOL stream and a weight percent concentration of 1% TOL between the C8A in the stream are entered into the column simulation. bottom of the column. The performance of the absorbed reboiler calculated from the simulation was 152.6 MMBTU / hr (44.7 MW). The temperature of the condensation vapors on the top plate of the column is 166.2 ° C, and the calculated condenser performance was 125.1 MMBTU / hr (36.7 MW), enough to reboil the benzene column.

[0067] The bottom streams of the toluene column are passed to a simulated xylene (XS) separator column to have 122 theoretical stages with feed to theoretical stage 91 from the top. As in Example 1, a design specification is introduced in the simulation of the xylene separator column of a weight percent concentration of 1% C8A in the bottom stream of the C9A + column. But, since the crystallization unit can tolerate a higher concentration of A9 + in the feed for crystallization, the specification for A9 + in the A8 stream relaxes to a weight percent concentration of 1% A9 +. This reduces the performance of the required absorbed reboiler calculated slightly to 107.0 MMBTU / hr (31.4 MW).

[0068] Thus, for this example, it is needed to operation of the combined absorbed reboiler 259.6 MMBTU / hr (76.1 MW) to the column and the column TOL XS to perform the desired separation of the stream bottom of the benzene column in a TOL stream, a C8A stream and an A9 + stream where the C8A stream contains a weight percent concentration of 1% TOL and 1 A9 + so that this stream can be sent directly to a crystallization unit for pX separation.

[0069] the A9 + stream can be directed to an A9 column that can produce an upper plate stream that includes A9 and some A10 that can be recycled to a TOL / A9 + TA unit, and a lower stream that includes C10 + and that it is substantially free of A9 which can be used as, for example, a fuel.

EXAMPLE 3: Separation scheme to produce an A8 stream suitable for direct delivery to a pX recovery unit by selective absorption

[0070] The separation scheme for this Example is shown in Figure 2, and was simulated through ASPEN. The design of the benzene and stabilizer columns is the same as in Examples 1 and 2. Various combinations of the design parameters have been implemented for the pre-fractionation and side discharge column. The combinations of design variables with the corresponding behavioral parameters are summarized in Table 3 for some cases in which energy savings can be achieved with respect to Example 1 complying with the specifications of a percentage concentration by weight of less than 1.5 % TOL and less than 500 ppmw of A9 + in the A8 stream, so that the A8 stream can be sent to a selective absorption unit for pX separation without the need for additional fractionation. The combined absorbed operation of the pre-fractionation columns (PREFRAC) and side discharge (SD-COL) of Example 3 represents the operation necessary to separate the bottom streams from a Bz column into a TOL stream suitable for recycling to the TOL / reactor. A9 +, an A9 + stream, and an A8 stream that can be sent directly to a selective absorption unit for pX recovery without the need for additional fractionation. the A9 + stream can be directed to an A9 column that can produce an upper plate stream that includes A9 and some A10 that can be recycled to a TOL / A9 + TA unit, and a lower stream that includes C10 + and is substantially free of A9 that can be used as, for example, a fuel.

[0071] Tables 3 and 4 show examples of design variables. "SD-COL, # of Stages" is the number of theoretical stages for this column in the simulation, including one stage for the reboiler and one for the condenser. "SD-COL, Stage-RFLX1" is the lateral discharge column in which a liquid lateral discharge is taken for reflux into the pre-fractionation column. "SD-COL, Stage-OVHDV1" is the stage in the side discharge column to which the steam from the top plate of the pre-fractionation column is directed. "SD-COL, Stage-BTTMLIQ1" is the stage in the side discharge column to which the liquid from the downstream of the pre-fractionation column is directed. "SD-COL, Stage-C8A" is the stage of the lateral discharge column from which the C8A is taken as lateral discharge.

T l. V ri l i ñ r l E m l

(continuation)

(3300 Ibmol / hr equals 1497 kmol / hr and 1 MMBTU / hr equals 0.293 MW.)

[0072] As the data in Table 3 shows, the fractionation scheme of this disclosure can reduce the energy consumption required to make the separation by more than 10%.

EXAMPLE 4: Separation scheme to produce an A8 stream suitable for direct delivery to a pX recovery unit by crystallization

[0073] The separation scheme for this example is shown in Figure 2, and was simulated through ASPEN. The benzene column and stabilizer designs are the same as in Examples 1 and 2. The top plate pressure of the SD-COL is assumed to be 62.3 psia (430 kPa absolute) with a pressure drop assumed 5 psi (34.5 kPa) through the condenser. Various combinations of the design parameters have been implemented for the pre-fractionation column (PREFRAC) and lateral discharge (SD-COL). The combinations of design variables with the corresponding performance parameters are summarized in Table 4 for some cases in which energy savings can be achieved with respect to Example 2 by complying with the specifications of a percentage concentration by weight of less than 1.0 % TOL and less than 1% A9 + in the A8 stream, so that the A8 stream can be sent to a crystallization section for pX separation without the need for additional fractionation. the A9 + stream can be directed to an A9 column that can produce an upper plate stream that includes A9 and some A10 that can be recycled to a TOL / A9 + TA unit, and a lower stream that includes C10 + and is substantially free of A9 that can be used as, for example, a fuel.

(1 MMBTU / hr equals 0.293 MW.)

[0074] As the data in Table 4 shows, the fractionation scheme of this disclosure can save almost 25% of the energy required in Example 2.

[0075] Note that the energy requirements to meet the A8 side discharge current specifications needed to supply a pX crystallization section for the cases in Example 4 are less than the energy requirements to meet the discharge current specifications side of A8 required to introduce A8 current into a selective absorption section of pX. Note also that fewer steps are needed for Example 4 than for Example 3. Reboiler operation is related to steam and liquid traffic in the tower. As the performance requirements for Example 4 are less than for Example 3, smaller diameter columns are required. Less operation also means less emission of greenhouse gases CO ² .

EXAMPLE 5: Separation scheme to produce an A8 stream suitable for direct delivery to a pX recovery unit by crystallization with increased SD-COL column pressure to produce medium pressure steam

[0076] The separation scheme for this Example is shown in Figure 2, and was simulated through ASPEN. For this case, the pressure of the PREFRAc and SD-COL columns was increased to allow the production of medium pressure steam (10 barg) from the condensation vapors of the upper plate of the SD-COL column. The top plate pressure of the s D-COL is assumed to be 116.8 psia (805 kPa absolute) with an assumed pressure drop of 5 psi (34.5 kPa) through the condenser. This gives a temperature of the upper plate of the column SD-COL inlet into the condenser of 203 ° C, and a condenser outlet temperature of about 201 ° C, enough to generate a vapor of 10 barg, which has a temperature of saturation of about 185 ° C. These condenser temperatures are also sufficient to reboil the benzene column, which has a lower flow temperature of about 150 ° C, and sufficient to boil the stabilizer column, which has a lower flow temperature of 185 ° C.

[0077] The design of the benzene and stabilizer columns is the same as in Examples 1 and 2. Various combinations of the design parameters have been implemented for the PREFRAC and SD-c Ol columns. The combinations of design variables with the corresponding performance parameters are summarized in Table 5 for some cases in which energy savings can be achieved with respect to Example 2 by complying with the specifications of a percentage concentration by weight of less than 1.5 % TOL and less than 1.5% A9 + in the A8 stream, so that the A8 stream can be sent to a crystallization unit for pX separation without the need for additional fractionation. the A9 + stream can be directed to an A9 column that can produce an upper plate stream that includes A9 and some A10 that can be recycled to a TOL / A9 + TA unit, and a lower stream that includes C10 + and is substantially free of A9 that can be used as, for example, a fuel.

T l. V ri l i ñ r l E m

(continuation)

(1 Ibmol / hr equals 0.454 kmol / hr and 1 MMBTU / hr equals 0.293 MW.)

[0078] As shown in the data in Table 5, for all these cases, the total performance of the PREFRAc and SD-COL columns is 10.2% lower than the total performance of the TOL and XS columns of Example 2 . When credit is given for the export of MP steam, the net energy required to perform the separation is less than half that of Example 2.

EXAMPLE 6: Separation scheme to produce an A8 stream suitable for direct delivery to a pX recovery unit by crystallization with increased SD-COL column pressure to produce medium pressure steam and with a C9A + stream of additional side discharge column.

[0079] The separation scheme for this Example is shown in Figure 3, and was simulated through ASPEN. The conditions and design for the stabilizer, benzene column, pre-fractionation column, and side discharge column are the same as for Example 5 Case 5.3 (as shown in Table 5) with the exceptions mentioned below.

[0080] In Example 5, the side discharge column had 90 theoretical stages, and a stream including A9 + was taken as the bottom stream. the A9 + stream from Example 5 can be directed to an A9 column that can produce an upper plate stream that includes A9 and some A10 that can be recycled to a TOL / A9 + TA unit, and a lower stream that includes C10 + and that it is substantially free of A9 which can be used as, for example, a fuel.

[0081] In this Example 6, a stream including mainly A9 and some A10 is taken as the additional side discharge stream (stream 301 of Figure 3) for recycling to the TOL / A9 + Ta reactor, and the bottom stream of the side discharge column (stream 302 of Figure 3) that includes C10 + and is substantially free of A9 and can be used as, for example, a fuel. In this example, the current that mainly includes A9 and some A10 is called the C9A + current. The additional lateral discharge (stream 301) is taken as liquid from the theoretical stage 90 from the top. Additional stages are added under this lateral discharge, which increases the total number of theoretical stages to the number shown in Table 6. Other relevant stages of the lateral discharge column remain the same as in Example 5 Case 5.3. The operation of the reboiler of the pre-fractionation column and the side discharge column were set based on Example 5 Case 5.3 at 130 MMBTU / hr (38.1 MW) and 105 MMBTU / hr (30.8 MW) respectively. Thus, in Example 6, the separation of the C9A + current occurs without additional operation relative to Example 5 Case 5.3.

[0082] To avoid the need for a separate A9 column, it is desirable that the C9A + stream contain essentially all of the MEB and TMB in the combined C9A + and C10 + streams, and a high fraction of DEB, DMEB and TTMB. However, it is desirable to separate a high fraction of naphthalene in the combined C9A + and C10 + streams in the C10 + stream since naphthalene and heavy components in the C10 + stream can vitiate the exchangers within the TA unit of TOL / A9 + and lead at a high rate of catalyst deactivation from the TA unit.

[0083] Simulation results for various cases are provided in Table 6.

T l. R l im l i n r l E m l.

[0084] As shown in this example, the recovery of the desirable MEB and TMB components in the CA9 + stream for recycling to a TOL / A9 + reactor may be close to 100%. The recovery of the desirable DEB, DMEB and TTMB components can also be very high. Naphthalene recovery in the stream C9A + is quite low and, therefore, a high fraction of naphthalene is recovered in the C10 + stream. Recovery of the desirable MEB, TMB, DEB, DMEB, and TTMB components in the C9A + stream increases with the specified recovery of TTMB in the C9A + side discharge stream. However, the recovery of naphthalene in this stream also increases. Naphthalene recovery also increases with a reduction in the number of stages added under the C9A + side discharge stream. Those of skill in the art will appreciate that the ideal number of stages and recovery of TTMB will depend on local prices of by-products and raw materials, energy cost and local cost of capital.

[0085] Although the invention has been described above according to different embodiments, it can be modified within the scope of this disclosure as long as it falls within the limits of the following claims. Therefore, the application is intended to cover various variations, uses or adaptations of the invention as claimed using the general principles disclosed in this invention. Furthermore, the application is intended to cover such deviations from the present disclosure that take place with the evolution of knowledge or standard practice in the art to which this invention belongs and which falls within the limits of the following claims.

Claims (18)

1. Procedure comprising the steps of: (a) supplying a pre-fractionation column feed stream comprising toluene, C8 aromatics and C9 + aromatics to a reboiled pre-fractionation column to produce an upper stream of the pre-fractionation column and a lower stream of the pre-fractionation column; and (b) supplying a pre-fractionation column top stream and a pre-fractionation column bottom stream to a side discharge column to produce a side discharge column top stream comprising toluene, and a column side stream lateral discharge comprising aromatics C8. 2. The method of claim 1, further comprising producing a lateral discharge column undercurrent including C9 + aromatics. The method of claim 1, further comprising producing a second side discharge column side stream comprising A9 for recycling to a TOL / A9 + transalkylation reactor without further fractionation, and a bottom column stream C10 + side discharge containing a weight concentration of less than about 2% A9. The method of claims 1 to 3, further comprising recovering the paraxylene from the first side stream from the side discharge column including C8 aromatics to produce a paraxylene product stream and a paraxylene lean stream. The method of one of claims 1-4, further comprising, before step (a): supplying a feed stream from the benzene, toluene, C8 aromatics, and C9 + aromatics to a benzene column to produce an upper stream from the benzene column comprising benzene and a lower stream from the benzene column comprising toluene, C8 aromatics and C9 + aromatics, where the bottom stream of the benzene column is the feed stream of the pre-fractionation column. 6. The method of claim 5, wherein the benzene column feed stream is obtained by providing a stabilizer column feed stream including volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics to a stabilizer column for produce an upper stabilizer column stream (s) including volatile fractions and a lower stabilizer column stream (s) including benzene, toluene, C8 aromatics and C9 + aromatics, where the bottom stream of the stabilizer column is the feed stream of the benzene column. 7. The process of claim 6, further comprising mixing a transalkylation reactor effluent stream including volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics with a paraxylene unit stream including benzene and toluene to produce the stabilizer column feed stream, preferably where the stabilizer column feed stream has been preheated. The method of claim 5, wherein the side discharge column operates at a pressure above atmospheric pressure, such that condensation vapors from the top stream of the side discharge column are used to reboil the benzene column. . 9. The method of claim 6, wherein the side discharge column operates at a pressure above atmospheric pressure, such that condensation vapors from the top stream of the side discharge column are used to reboil the stabilizer column. 10. An apparatus comprising: (a) a boiled pre-fractionation column to receive a pre-fractionation feed stream comprising toluene, C8 aromatics, and C9 + aromatics and producing an upper stream from the pre-fractionation column and a lower stream from the pre-fractionation column; Y (b) a side discharge column for receiving the top stream from the pre-fractionation column and the bottom stream from the pre-fractionation column and producing a top stream from the side discharge column comprising toluene, and a first side stream from the side discharge column comprising C8 aromatics. The apparatus of claim 10, wherein the side discharge column further produces a bottom discharge column stream comprising C9 + aromatics, or where the side discharge column further produces a second column stream side discharge comprising A9 for recycling to a TOL / A9 + transalkylation reactor without additional fractionation, and a bottom stream from the C10 + side discharge column containing a weight percent concentration of approximately 2% A9. 12. The apparatus of claim 10 further comprising a benzene column for receiving a benzene column feed stream comprising benzene, toluene, C8 aromatics and C9 + aromatics and for separating the feed stream from the benzene column. benzene in an upstream benzene column comprising benzene and a downstream benzene column comprising toluene, C8 aromatics and C9 + aromatics; where the bottom stream of the benzene column is the feed stream of the pre-fractionation column; and preferably further comprising a stabilizer column to receive a stabilizer column feed stream comprising volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics, and producing an upstream stabilizer column stream comprising volatile fractions and a stream lower of the stabilizer column including benzene, toluene, C8 aromatics and C9 + aromatics; where the bottom stream of the stabilizer column is the feed stream from the benzene column, or further comprising a mixer for mixing a effluent stream from the transalkylation reactor comprising volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics with a Paraxylene unit stream comprising benzene and toluene to produce the stabilizer column feed stream. The apparatus of one of claims 10 to 12 further comprising a paraxylene recovery section for recovering paraxylene from a side stream from the side discharge column comprising C8 aromatics, preferably where the paraxylene recovery section comprises a selective paraxylene absorption unit, or preferably where the paraxylene recovery section comprises a crystallization unit. The apparatus of one of claims 10 to 13 further comprising a transalkylation reactor for reacting a reactor feed stream comprising toluene and optionally C9 + aromatics to produce a transalkylation reactor effluent stream comprising fractions volatiles, benzene, toluene, C8 aromatics and C9 + aromatics. 15. The apparatus of one of claims 10-14, wherein the side discharge column receives the top stream from the pre-fractionation column as a stream of steam without condensation, and / or where the pre-fractionation column and side discharge column they share a common frame with a dividing wall. 16. The method according to claim 1, comprising the steps of: (i) reacting in a transalkylation reactor a reactor feed stream comprising toluene and optionally C9 + aromatics to produce a effluent stream of the transalkylation reactor comprising volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics; (ii) optionally mixing the effluent stream from the transalkylation reactor with a stream from the paraxylene unit comprising benzene and toluene to produce a stabilizer column feed stream comprising volatile fractions, benzene, toluene, C8 aromatics and C9 + aromatics ; (iii) separating the stabilizer column feed stream into a stabilizer column to produce an upper stabilizer column stream comprising volatile fractions and a lower stabilizer column stream comprising benzene, toluene, C8 aromatics and C9 + aromatics; (iv) separating the bottom stream from the stabilizer column into a benzene column to produce a top stream from the benzene column comprising benzene and a bottom stream from the benzene column comprising toluene, C8 aromatics and C9 + aromatics; (v) supplying a lower stream from the benzene column to a revolving pre-fractionation column to produce an upper stream from the pre-fractionation column and a lower stream from the pre-fractionation column; (vi) supplying a top stream from the pre-fractionation column and a bottom stream from the pre-fractionation column to a side discharge column to produce a top stream from the side discharge column comprising toluene, and a first side stream from the column side discharge comprising C8 aromatics; (vii) recovering paraxylene from the side stream of the side discharge column including C8 aromatics; Y (viii) recovering the benzene from the upper stream of the benzene column, where at least a part of the upper stream from the side discharge column is recycled into the transalkylation reactor. The method of claim 16, wherein the side discharge column further produces a bottom discharge column stream comprising C9 + aromatics where at least a portion of this stream is recycled in the transalkylation reactor, or where the column side discharge receives the upper stream from the pre-fractionation column as a steam stream without condensation, or where the Prefractionation and the side discharge column share a common frame with a partition wall. 18. The method of claim 16 further comprising producing a stream from the second side of the side discharge column comprising A9, where at least part of it is recycled into a TOL / A9 + transalkylation reactor without fractionation downstream, and a C10 + lateral discharge column downstream stream containing less than 2% weight percent concentration of A9; optionally further comprising operating the side discharge column at a pressure above atmospheric pressure and reboiling the benzene column by condensing at least a portion of the top stream from the side discharge column; or optionally further comprising generating the stream from the condensation of at least a portion of the top stream from the side discharge column.